Or turn the question around: Why are there no WORS races in Northwest WI?

EauClaire is the closest and that hardly counts as northern WI being south of highway 29.
River Falls (White Tail Ridge) was at least western, but not much further north, had good attendance, but no longer is on the schedule.

The further WORS goes from the Madison Milwaukee Metro area's the lower rider turnout - I mean the less money WORS makes...

Fun fact - MNMTB likes racing at White Tail Ridge in Riverfalls WI so much that it's the MN State Championship race for MN in 2014 - Go Figure. This event has historically been the highest attended event for MNMTB since WORS ditched it.